The present invention concerns an aqueous colorant. More particularly, the invention concerns an aqueous colorant for incorporation into plastics and a method for use of such an aqueous colorant.
Traditionally, color has been incorporated into plastic materials by a variety of different methods. These methods include (i) pre-colored plastics which mix pigments and/or dyes with a polymer melt in a compounding process (ii) pellet concentrate where a dry color containing pellet is mixed with an uncolored virgin resin at the process equipment (iii) dry color concentrates which can be added to process equipment while making the finished parts, and (iv) liquid color concentrates where pigments are mixed with an organic liquid carrier.
When developing a product to color thermoplastic resins, the skilled artisan will consider the handling, storage, incorporation and dispersion characteristics of a delivery system. Each of the above described colorant systems provide advantageous characteristics. However, each colorant system also demonstrates drawbacks.
With respect to solid systems, handling, precision and cleanliness of the work environment are concerns. For example, the effect of the carrier resin on the characteristics of the colored thermoplastic resin can be a concern in pellet based systems. Similarly, solid colorants often do not uniformly mix with the plastic, do not disperse uniformly during molding, and can segregate from the plastic during pre-molded handling.
To address some of these concerns, some artisans use colorant dispersion phase transfer pigments from an aqueous to a non-aqueous phase, in discrete form, while still in an unconcentrated slurry through preferential wetting by surface contact between the pigment and a hydrophobic polymer solution emulsified in water. This material can then be concentrated in a plate and frame press or by flocculation, flotation or settling. After filtration, the resultant material (xe2x80x9ca phase-transferred presscakexe2x80x9d) somewhat resembles conventional presscake, but contains an organic phase as well as only 10 to 45 percent water, whereas conventional presscake contains 55 to 90 percent water. This type of pigment-hydrophobic organic vehicle product is disclosed in U.S. Pat. No. 4,634,471. Importantly, the emulsion and the pigment slurry mixture is forced through a concentration zone and flushed with a hydrophilic organic vehicle. Accordingly, introduction of the colorant to the plastic material is via a liquid organic medium.
Liquid color concentrates have also become increasingly attractive to overcome the drawbacks of traditional solid colorants. For example, in U.S. Pat. No. 3,956,008, a liquid colorant dispersion for plastics is disclosed which is comprised of 5-70 weight percent colorant and 95-30 weight percent vehicle. The vehicle is stated to be comprised of two major components, 1) from 5-25 weight percent of a physically-active, chemically-inert solid in the form of fine particles, and 2) from 95-75% of a surfactant system. The preferred surfactant system is stated to be a sorbitan ester surfactant, such as sorbitan trioleate. The applicability of this system, however, has been substantially limited because the carrier may experience pigment settling, incompatibility with the host polymeric material, insufficient heat stability causing processing problems, interference with the mechanical and physical properties of the end-product, or any combination of these undesirable factors.
Several techniques have also been developed in order to better achieve uniform dispersion and storage stable liquid colorant concentrates. For example, U.S. Pat. Nos. 3,956,008 and 4,167,503 disclose colorants having surfactant based vehicles that improve pigment dispersion and allow relatively high pigment loadings at viscosities suitable for use in standard in-line metering equipment. In the ""503 patent, a liquid carrier system for dispersing into polymeric compositions is disclosed as comprised of an alkylated phenoxy poly(ethyleneoxy) ethanol carrier wherein the alkyl moiety of the ethoxylated phenol is selected from the group consisting of phenols and substituted phenols and a colorant in an amount from 0. 1% to 80% based on the weight of the carrier.
U.S. Pat. No. 4,341,565 discloses a liquid gel colorant that comprises a suspension of organic pigments in a liquid vehicle that is a plasticizer and which is gelled by an organophilic, expanding lattice clay that is ion exchanged with alkyl ammonium ions. The gel is modified by the addition of certain hydroxyalkyl fatty amines or fatty imidazolinium quaternaries, while the plasticizer is stated to be, for example, esters of saturated mono- or di-basic alcohols or tri-basic, saturated aliphatic or aromatic acids, or phosphoric acids.
In U.S. Pat. No. 4,571,416, a polyolefin compatible liquid colorant concentrate is disclosed that is a dispersion of a colorant and/or other additive in a non-surfactant based vehicle. The vehicle includes a low molecular weight addition polymer and an essentially non-volatile solvent for the low molecular weight addition polymer. The vehicle may also contain a dispersion aid, such as oleic acid, especially when the colorant is an inorganic pigment. The concentrate is stated to be comprised of a vehicle containing a low molecular weight addition polymer, such as polybutylene, polystyrene, polyalpha-methyl styrene/vinyl toluene copolymer or an acrylic copolymer and an essentially non-volatile solvent for the low molecular weight polymer which has a boiling point of at least about 450xc2x0 F.
Turning next to U.S. Pat. No. 5,308,395, a liquid concentrate for incorporation into polymeric resins is disclosed as comprised of a vehicle of at least one organic rosin material, at least one surfactant, and at least one colorant or additive.
U.S. Pat. No. 5,759,472, provides a rare disclosure of a liquid color system including even a minor amount of water. More particularly, the liquid color system includes from about 10% to about 75% by weight carrier, from about 0% to about 15% by weight water, from about 0.01% to about 10% by weight dispersant, and from about 10% to about 80% by weight colorant. The carrier is stated to be a material selected from the group consisting of propylene glycol, ethylene glycol, diethylene glycol, tri(ethylene glycol), glycerine, and mixtures of such materials.
Accordingly, liquid colorant systems have relied on an organic vehicle. Thus, there has previously been no disclosure of an aqueous based system for use as a color concentrate for the coloration of plastic material. This focus on organic vehicles in the art may arise because in injection molding, for example, a common surface defect in molded parts is xe2x80x9csplay,xe2x80x9d which is the result of moisture in the resin. Splay is eliminated by drying the resin in an oven or hopper dryer prior to use. Similarly, steam generated from moisture can cause foaming in parts that reduces strength. Accordingly, there is no motivation in the art, and in fact, a recognized reason to avoid use of any material in treating plastics which contains significant quantities of water.
Of course, this perception has been carried forward to liquid colorant systems, which as shown above, rely on organic vehicles. Notwithstanding this prior reluctance to utilize water in liquid colorant systems, the present invention is directed to an aqueous based liquid colorant system demonstrating an excellent ability to color various thermoplastic materials in many commonly used molding or extrusion operations.
The present invention provides a new and improved liquid colorant system that is designed for the coloring of plastics. The invention more particularly relates to a liquid colorant system comprised of a colorant, a dispersant and at least 25% water. The colorant system is particularly suited to use in injection molding, extrusion, blow molding and rotational molding of plastic materials.
It is an advantage of the present invention to achieve a higher pigment loading than organic systems.
It is a further advantage of the present invention to achieve higher color strength for many pigments.
It is a further advantage of the present invention to achieve better color incorporation, temperature uniformity, better shelf stability and reduced screw slippage in extruders.
It is a further advantage of the present invention to provide an aqueous colorant that adheres well to resin pellets, even after water flash-off, without creating a significant powder build up in a premixer
The foregoing and other features of the present invention are hereinafter more fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the present invention may be employed.
The liquid color system of the present invention comprises a dispersant, a colorant and water. The system may optionally also contain other traditional additive(s). Specifically, the present invention is directed to a liquid colorant system comprised of at least 10 to 80%, preferably 30 to 70% of a pigment or dye, at least greater than 0, preferably 0.5 to 30%, and more preferably 10 to 20% dispersant, and the balance water and other traditional additive(s). Preferably, at least 30%, more preferably, 40% of the liquid colorant system will be comprised of water and at least 40%, more preferably at least 50% will be colorant.
The term xe2x80x9ccolorantxe2x80x9d when used throughout this specification and in the appended claims, denotes any conventional inorganic or organic pigment, dyestuff, or carbon black. Those skilled in the art will be aware of suitable inorganic pigments, organic pigments and dyestuffs. Such materials are described, for example, in Kirk Orthmer Encyclopedia of Chemical Technology, Third Edition, vol. 19, pp. 1-78 which is incorporated by reference herein; however, examples include:
(1) inorganic types such as titanium dioxide, carbon black, iron oxide, zinc chromate, cadmium sulfides, chromium oxides, sodium aluminum silicate complexes, such as ultramarine pigments, metal flakes and the like; and
(2) organic types such as azo and diazo pigments, phthalocyanines, quinacridone pigments, perylene pigments, isoindolinone, anthraquinones, thioindigo, solvent dyes and the like.
Accordingly, this invention may be employed in conjunction with the. production of many different pigments. Since the scientific nomenclature for dyes and pigments is very difficult, trade names are used extensively in speaking of them. In this regard, examples of pigments for which this invention is applicable include but are not limited to: Pigment Red 1, Pigment Red 3, Pigment Red 4, Pigment Red 48:1, Pigment 48:2, Pigment Red 48:4, Pigment Red 49:1, Pigment Red 49:2, Pigment Red 53:1, Pigment Red 52, Pigment Red 57, Pigment Red 81, Pigment Red 190, Pigment Orange 13, Pigment Orange 19, Pigment Orange 46, Yellow 12, Pigment Yellow 13, Pigment Yellow 14 Pigment Yellow 17, Pigment Yellow 27, Pigment Yellow 83, Pigment Green 7, Pigment Green 36, Pigment Blue 6, Pigment Blue 15:3, Pigment Blue 61.
The dispersant, alternatively referred to as a surfactant, that is utilized in the liquid color system is dependent upon the type of colorant being used. Moreover, the primary requirement is that the dispersant is soluble in the carrier (i.e. water) and it associates strongly with the particles of colorant as they are separated from each other during mixing, thereby preventing the particles from reattaching to each other during storage and use. Examples of suitable dispersants include polyvinylpyrrolidone (e.g., Sokalan HP50 from BASF), sodium salt of polyacrylic acid (molar mass from 1,200-250,000), sodium/iron salt of lignosulfonic acid, sodium salt of condensed naphthalenesulfonic acid, sodium naphthalene sulfonate and sodium or ammonium salts of polymeric carboxylic acid, amine alkyl sulfonates, bis-ridecyl esters of sodium sulfosuccinic acid, block copolymers of ethylene oxide and propylene oxides as well as many others. Additional examples of surface active agents which may be employed are the sodium salts of high molecular weight fatty alcohol sulfates, such as sodiumlauryl sulfate, sodium lignin sullfonates, the dioctyl ester of sodium sullfosuccinic acid, polyalkylene oxide condensation products, such as polyethylene oxides, quaternary ammonium salts, the sodium sulfonates of oleic acid esters of aliphatic compounds, sodium salts of aryl alkyl polyether sulfonates, and the like.
Preferably, the dispersing agent (alternatively referred to as a surfactant) will be non-ionic such as those selected from nonyl-phenols, octyl-phenols, acetylenic diols, or ethoxylated sorbitol esters. However, the dispersant can also be anionic such as any of those known to the skilled artisan. In fact, the invention is not intended to be limited to any specific dispersant agent. Rather, any suitable compound which increases the stability of the pigment/dye in water is suitable.
The concentrates of the present invention may be used to color or incorporate additives into a wide variety of polymeric resins but finds particular application in modification of thermoplastic resins. For example, the color concentrates of the invention are generally compatible with, and may be used with, but not limited to, the following resins: polyolefins such as LLDPE, HDPE, LDPE, homopolymer and copolymer polypropylenes, EVA, etc.; styrenics such as crystal polystyrene, HIPS, MIPS, etc.; copolymer resins, resin blends and alloys such as ABS, polyphenylene ether (including PPO blends such as NORYL(copyright), various engineering polymer alloys; polyamide resins, such as Nylon 6, 6/6, 11, 12, copolymers, terpolymers, etc.; acrylic resins, polycarbonates, and other amorphous resins; polyesters, such as PET, PBT, and othersxe2x80x94both thermoplastic and curing, as well as resins reinforced with glass, quartz, carbon, aramid, or the like, fibers.
Typical examples of the additives which are suitable for use with the carrier of this invention include:
Antistatic Agents. Suitable are those products which are stable at temperatures above 200xc2x0 C.
UV Stabilizers. Such as benzophenones, benzotriazoles, sterically hindered amines, and other types.
Flame Retardants. Such as phosphate esters, halogenated organic and inorganic materials, aluminum and antimony oxides, and the like.
Heat Stabilizers. Organo-tins, calcium, barium, strontium/tin, barium.cadmium/zonc phosphites, and the like.
Mold Release/Lubricants/Slip Agents. Metal stearates and stearic acid, silicone oils, glycerol and polyglycerol esters, amides, derived from fatty acids, and others.
Foaming Agents. Tetrazole type, trihydrazide triazine type, hydrazine derivatives, p-oluene sulfonyl semicarbazide, and many others.
Filler Reinforcing Materials. Calcium carbonates, aluminum trihydrate, silica and silanes, mica, glass fibers, asbestos, and others.
Suspending Agents. Such as organo-clays.
Thickeners. Such as ethyl cellulose.
Binding Agents. Such as solution acrylic polymers, ethyl cellulose, acrylic latex polymers, polyurethane latex or emulsion polymers.
The invention provides minimal impact on the molding systems with the aqueous system, in contrast to what would previously have been expected. More particularly, it was not realized that the water would vaporize off rapidly and not effect the system in a negative manner, and in fact, have less impact than many organic vehicle systems. Similarly, the near 100% volatilization of the aqueous carrier system does not effect the overall characteristics of the final molded product. In contrast, traditional organic vehicles are typically not 100% volatilized and therefore are present in the polymer and provide or create undesirable characteristics therein.